Catalyst structure with catalyst particles forged into substrate surface

ABSTRACT

A catalyst structure has catalytic particles dispersed over and forged into the surface of a metal substrate such that the particles protrude from the surface and are permanently fixed into the surface. The forging is accomplished by brush graining to press the particles into the surface The particles may be any particles which have catalytic activity for a particular purpose and which are hard enough to forge into the metal substrate.

[0001] This application is a continuing application of U.S. ApplicationSer. No. 09/590,736 filed Jun. 8, 2000 and titled Method of FormingCatalyst Structure With Catalyst Particles Forged Into SubstrateSurface.

Background of the Invention

[0002] The present invention relates to a catalyst structure comprisinga substrate having protruding catalyst particles permanently fixed intothe surface of the substrate.

[0003] Catalyst structures have been disclosed in the prior art whichinvolve the placement of catalyst materials onto the surface of asubstrate. At least one of the uses for these prior art catalyticstructures is for the conversion of atmospheric ozone to molecularoxygen as well as the conversion of other airborne pollutants such ascarbon monoxide and unburned hydrocarbons into harmless compounds suchas carbon dioxide and water vapor. One particular use has been for theconstruction of automotive heat exchangers such as radiators and airconditioning condensers.

[0004] U.S. Pat. No. 4,206,083 discloses the co-precipitation ofplatinum, palladium and manganese oxide on a ceramic support forming acatalyst for the decomposition of ozone in air. The ceramic support isimpregnated with a solution containing the precursors of the desiredcatalyst. The impregnated support is then dried and heated to produceplatinum and palladium metal and manganese oxide.

[0005] In U.S. Pat. No. 4,343,776, an ozone abatement catalyst isdescribed having a carrier or support of a porous refractory skeletalstructure or metal monoliths of aluminum or other materials preferablyhaving a plurality of flow-through channels. A platinum group metal anda non-precious Group VIII metal oxide or aluminate, such as an oxide oraluminate of iron, cobalt and nickel, are applied to the externalsurface of the carrier or support with the metal oxide or aluminatebeing applied with an alumina slip preferably prior to the applicationof the platinum group metal.

[0006] U.S. Pat. No. 5,187,137 likewise discloses an ozone decomposingcatalyst comprising a manganese oxide together with palladium orpalladium oxide formed as a thin film on a support. The support may beformed from various metal oxides or it may be a metal support. Thecatalyst is applied to the support as a thin film preferably with analumina sol as a binder.

[0007] Another catalyst composition which is described as being adaptedfor ozone abatement is disclosed in U.S. Pat. No. 5,422,331. Thiscatalytic material comprises a substrate, which may be aluminum, with anundercoat layer containing a mixture of fine particulate refractorymetal oxide and a sol such as a silica sol providing good adherence tothe substrate. An overlayer also contains a refractory metal oxide onwhich is dispersed a catalytic metal component, such as palladium andmanganese components, which is then calcined.

[0008] U.S. Pat. 5,997,831 specifically discloses a method of treatingthe atmosphere to convert pollutants such as ozone, hydrocarbons andcarbon monoxide to harmless compounds involving contacting theatmosphere with a heat exchanger which has an outer surface coated inselected areas with a catalytic layer. The catalyst may be manganeseoxide and/or precious metals applied by dipping or spraying and thecatalytic layer is coated with a porous protective coating such as apolymer.

Summary of the Invention

[0009] The present invention relates to a catalytic structureparticularly suited to the treatment of the atmosphere to removeatmospheric pollutants. The invention relates specifically to catalystsfor the decomposition of ozone to form molecular oxygen but is alsoapplicable to catalyst materials for a range of other reactionsincluding, for example, the decomposition of hydrocarbons and theoxidation of carbon monoxide. An object of the invention is to provide ametal substrate having a surface with catalyst particles dispersed overand fixed to the surface.

[0010] The invention involves a catalytic structure having catalyticparticles dispersed over and forged into the surface of a substratemember whereby the particles are protruding from and permanently fixedto the substrate. The substrate is a metal sheet or body, preferablyaluminum or copper, and the catalytic structure is formed by passingthis substrate through a slurry of catalyst particles which are capableof being forged into the surface of the substrate. As the substrate ispassing through the slurry, the catalyst particles are pressed againstthe surface of the substrate to fixedly forge the particles into thesurface. The substrate is preferably in web form and is passedcontinuously through the slurry. Pressing the particles against thesurface is preferably accomplished with a rotating graining brush. Thecatalyst particles may comprise any particulate material which iscatalytic for the intended purpose and which is capable of being forgedinto the substrate surface.

Description of the Preferred Embodiments

[0011] The catalyst structure has a substrate member which is a metalcapable of having catalyst particles forged into the surface. In thepreferred method of forming the catalyst structure, the substrate is aweb of the substrate material which is continuously processed to forgethe catalyst particles into the substrate and which may then be cut intodesired catalytic structural shapes. However, the substrate may also beindividual sheets or shaped members. The preferred substrate material isaluminum or copper but other metallic substrates can be used.

[0012] The particles for use in the present invention comprise anyparticulate material which is catalytic for the intended use, such asfor ozone decomposition, and which is capable of being forged into thesurface of the substrate. That is, the particulate catalytic materialmust be hard enough to be pressed and forged into the substrate surface.The preferred particles are manganese oxide particles because they arehard enough to forge and they are a particularly effective catalyst forozone decomposition. The manganese oxide may be manganese dioxide,manganic oxide or manganous oxide. However, the invention is not limitedto manganese oxide as the catalytic particles. Other examples of theparticulate material are other metal oxides and in particular thetransition metal oxides in so far as each one is catalytic for theparticular reaction and hard enough to forge into the substrate.Specific examples are copper oxide, nickel oxide, iron oxide, titaniumoxide, chromium oxide and zinc oxide.

[0013] In the present invention, the catalyst particles are forged intothe surface of the substrate from a slurry. By this forging action, theparticles actually penetrate into the surface and are firmly captured bythe forged substrate material but still substantially exposed at thesurface. Although an aqueous slurry is preferred for the forgingoperation, the slurry could be formed from any desired liquid.

[0014] In order to form the catalyst structure of the current invention,the forging of the particles into the substrate takes place in theslurry with the substrate being passed through the slurry and theparticles in the slurry being pressed against the substrate with a forcesufficient to forge the particles partially into the substrate such thatthe particles protrude from the surface and such that the particles arecaptured by and permanently fixed into the substrate. The preferredmethod is to continuously pass an elongated web of the substratematerial through the slurry although this method is equally applicableto the treatment of individual sheets of substrate or to specificobjects formed of the substrate material such as fan or propellerblades. As the substrate material passes through the slurry, thesubstrate is engaged by one or usually a series of rotating brusheswhich force the particles into the substrate. However, an excessivenumber of rotating brushes or an excessive number of passes through thebrushes will result in the particles being fully forged into thesubstrate whereby they no longer protrude from the surface resulting ina reduction in the catalytic efficiency. The rotating brushes are of thesame type as used for the brush graining of plates such as lithographicprinting plates.

[0015] Several factors impact on the selection of the specific operatingconditions for the forging process. The hardness and cutting nature ofthe catalytic particles being forged and the hardness of the metal oralloy being used as the substrate are significant factors. Eachcatalytic reaction will have an optimum size and distribution conditionfor the catalyst that will yield an optimum catalytic efficiency. Thusthe selection of variables such as the particle size, concentration ofparticles in the slurry, brush pressure and the rotation rate of thebrushes will vary with each specific application.

[0016] The catalyst structure of the present invention has a metalsubstrate with catalyst particles dispersed over at least one of thesurfaces of the substrate and with these catalyst particles beingpartially forged into the surface whereby they are fixed in place. Thispermits the structure to be handled, cut, shaped and fabricated intoproducts such as heat exchanger parts without destroying the catalyticsurface such as by spalling of a coating. The particles on the surfacealso increase the surface area and create turbulence which results inthe beneficial mixing of the air or other fluid flowing over the surfaceto increase the contact between the reactants and the catalyst.

1. A catalytic structure comprising oxide catalyst particles dispersedover and partially forged into a surface of a substrate wherein saidoxide catalyst particles are permanently fixed to said substrate andprotrude from said surface of said substrate wherein said catalyticstructure is produced by the process of: (a) providing a substrate; (b)forming a slurry of oxide catalyst particles of a composition capable ofbeing forged into a surface of said substrate; (c) applying said slurryto said surface of said substrate; and (d) rotating a graining brush inengagement with said surface of said substrate having said slurrythereon with a force sufficient to forge said oxide catalyst particlespartially into said surface and permanently fix said oxide catalystparticles to said substrate and leave said oxide catalyst particlesprotruding from said substrate.
 2. A catalytic structure as recited inclaim 1 wherein said oxide catalyst particles comprise an ozonedecomposing catalyst.
 3. A catalytic structure as recited in claim 2wherein said oxide catalyst particles comprise a manganese oxide.
 4. Acatalytic structure as recited in claim 3 wherein said manganese oxidecomprises manganese dioxide.
 5. A catalytic structure as recited inclaim 1 wherein said substrate comprises aluminum.
 6. A catalyticstructure as recited in claim 1 wherein said substrate comprises copper.7. A catalytic structure as recited in claim 1 wherein said oxidecatalyst particles are dispersed over and partially forged into oppositesurfaces of said substrate.
 8. A catalytic structure comprising oxidecatalyst particles dispersed over and partially forged into a surface ofa substrate wherein said oxide catalyst particles are permanently fixedto said substrate and protrude from said surface of said substratewherein said catalytic structure is produced by the process of: (a)providing a substrate web; (b) forming a slurry of oxide catalystparticles of a composition capable of being forged into a surface ofsaid substrate web; (c) applying said slurry to said surface of saidsubstrate web; (d) rotating a graining brush in engagement with saidsurface of said substrate web having said slurry thereon with a forcesufficient to forge said oxide catalyst particles partially into saidsurface and permanently fix said oxide catalyst particles to saidsubstrate web and leave said oxide catalyst particles protruding fromsaid substrate web; and (e) cutting said web into individual catalyticstructures.
 9. A catalytic structure as recited in claim 8 wherein saidoxide catalyst particles comprise an ozone decomposing catalyst.
 10. Acatalytic structure as recited in claim 9 wherein said oxide catalystparticles comprise a manganese oxide.
 11. A catalytic structure asrecited in claim 10 wherein said manganese oxide comprises manganesedioxide.
 12. A catalytic structure as recited in claim 8 wherein saidsubstrate comprises aluminum.
 13. A catalytic structure as recited inclaim 8 wherein said substrate comprises copper.
 14. A catalyticstructure as recited in claim 8 wherein said oxide catalyst particlesare dispersed over and partially forged into opposite surfaces of saidsubstrate.
 15. A catalytic structure comprising oxide catalyst particlesdispersed over and partially forged into a surface of a substratewherein said oxide catalyst particles are permanently fixed to saidsubstrate and protrude from said surface of said substrate.
 16. Acatalytic structure as recited in claim 15 wherein said oxide catalystparticles comprise an ozone decomposing catalyst.
 17. A catalyticstructure as recited in claim 16 wherein said oxide catalyst particlescomprise a manganese oxide.
 18. A catalytic structure as recited inclaim 17 wherein said manganese oxide comprises manganese dioxide.
 19. Acatalytic structure as recited in claim 15 wherein said substratecomprises aluminum.
 20. A catalytic structure as recited in claim 15wherein said substrate comprises copper.
 21. A catalytic structure asrecited in claim 15 wherein said oxide catalyst particles are dispersedover and partially forged into opposite surfaces of said substrate.